Quantum solitons and cluster states with well-defined atom number

超低温下的粒子可以显示出令人惊讶的量子效应，如隧道效应和纠缠。通常，这些量子效应对于单个粒子最强，但对于大型多体系统则会减弱。特别是玻色子的多体系统，即允许同时占据同一状态的粒子，可以用集体波函数很好地描述，具有与经典流体相似的性质。目前正在研究这种经典的，类似流体的制度和具有单个粒子的系统之间的交叉，并且观察量子效应所需的粒子数量正在积极辩论。该项目的目标是探测和研究超冷原子气体在这种交叉机制中的两种状态--“量子亮孤子”和大的“团簇态”。这两种状态预计将存在类似的实验参数之间的5和几百个原子，但他们接近交叉制度从相反的sides.Bright孤子是无色散波包，传播不改变其形状，他们提出了一个典型的非线性流体的属性。在粒子数减少的情况下，亮孤子有望获得单个量子物体特有的性质，如离散隧穿、不确定关系和纠缠。另一方面，团簇态是少数粒子的松散束缚态，类似于分子。随着粒子数的增加，它们预计会失去量子特性。该项目的目标是在实验上制备具有一定数量超冷原子的亮孤子和团簇态，并探索原子数变化时系统的性质。该研究将拓宽我们对少体和多体物理之间界限的理解，并有可能推进技术应用，例如随着基于大的和复杂的量子态的新量子技术的发展。

Particles at ultra-low temperatures can show surprising quantum effects, such as tunnelling and entanglement. Typically, those quantum effects are strongest for individual particles but decrease for large many-body systems. Especially many-body systems of bosons, i.e. particles which allow for a simultaneous occupation of the same state, are well described by a collective wave function, with similar properties as a classical fluid. The crossover between this classical, fluid-like regime and systems with individual particles is currently studied, and the particle number, required to observe quantum effects, is actively debated. The goal of this project is to detect and study two states of ultracold atomic gases in this crossover regime - "quantum bright solitons"' and large "cluster states". Both states are expected to exist for similar experimental parameters with between five and a few hundred atoms, but they approach the crossover regime from opposite sides.Bright solitons are dispersionless wave-packets that propagate without changing their shape, and they present a typical property of nonlinear fluids. For reduced particle number, bright solitons are expected to acquire properties which are characteristic for a single quantum object, such as discrete tunnelling, uncertainty relationships and entanglement. Cluster states on the other hand are loosely bound states of few particles, similar to molecules. They are expected to lose quantum properties with increasing particle number. The goal of the project is to experimentally prepare bright solitons and cluster states with a well-defined number of ultracold atoms, and to probe the properties of the system as the atom number is changed.The research will broaden our understanding of the boundary between few-body and many-body physics, and it has the potential to advance technical applications, e.g. with the development of new quantum technologies based on large and complex quantum states.